Method for removal of biofilm

ABSTRACT

The present invention provides a method for the removal of biofilm, flocculent bulked sludge or bulked biologically active sludge from an aqueous system. The method involves adding one or more chlorinated hydantoins, such as dichloro- or monochlorodialkylhydantoin, to the aqueous system. Alternatively, the chlorinated hydantoin may be formed in situ by adding a chlorine source and an alkylated hydantoin separately to the aqueous system. The invention is particularly advantageous because of the outstanding photostability of the chlorinated hydantoin solutions even when exposed to sunlight.

PRIORITY DATA

This application is a U.S. National Phase application of InternationalPatent Application No. PCT/US2003/017882 filed Jun. 6, 2003, whichclaims priority from U.S. Provisional Application Ser. No. 60/435,680filed Dec. 20, 2002, which is incorporated hereby by reference.

BACKGROUND OF THE INVENTION

Biofilm may be defined as an undesirable accumulation of microorganismson a surface and in flocculent masses. It is estimated that more than99% of all the planet's bacteria live in biofilm communities. Biofilmconsists of cells immobilized in a substratum, frequently embedded in anorganic polymer matrix of microbial origin, which can restrict thediffusion of substances and bind antimicrobials. In flowing aquaticenvironments, a biofilm consists of a sticky and absorptivepolysaccharide matrix encompassing microorganisms. Biofilm bacteria aremorphologically and metabolically distinct from free-floating bacteria.Their structural organization is a characteristic feature anddistinguishes biofilm cultures from conventional planktonic organisms.

Biofilms create problems for industry from corroding water pipes tocomputer-chip malfunctions. Any man-made device immersed in an aquatichabitat is susceptible to colonization by microbial biofilm. Forexample, biofilm may be present on the surfaces of ship bottoms,industrial pipelines, household drains, and artificial hip joints. Forthe industrial manufacturer, biofilm clusters represent a source ofmicrobial inoculation in a system and may cause plugging problems. Inwater treatment facilities, the formation of suspended biofilm producesa bulked biological sludge which settles poorly and is difficult tocompact in the clarification process. Both non-filamentous andfilamentous bulk forms are prevalent in which numerous bacteria permeatethe floc. In addition to their role as fouling agents, biofilms may alsohave adverse effects on people, including altering their resistance toantibiotics and affecting the immune system. Thus, there exists a needin the art for developing effective methods of removing biofilm.

The dynamic nature of biofilms makes it difficult to measure and monitorbiofouling. Biofilms often include embedded inorganic particles such assediments, scale deposits, and corrosion deposits. Moreover, biofilmscontinuously change in thickness, surface distribution, microbialpopulations and chemical composition, and respond to changes inenvironmental factors such as water temperature, water chemistry andsurface conditions. Thus, the complexity of biofilms has reduced theeffectiveness of treatment and removal strategies.

Even though most microorganisms in industrial systems are associatedwith biofilm, they have historically received less attention thanplanktonic microorganisms. However, it has been shown that variousbiocides are less effective against biofilm than dispersed cells of thesame organism. The most common biocides used in biofilm control are purefree halogen donors such as NaOCl and NaOCl/NaOBr. These, however, mustbe used in high quantities to be effective. In addition, several recentstudies evaluating halogen efficacy on biofilms showed an increaseddisinfection resistance of attached bacteria to free chlorine. Freechlorine treatment at concentrations usually effective againstplanktonic microorganisms has little effect on the number of attachedbacteria or on their metabolic activity. The data indicate that thetransport of free chlorine into the biofilm is a major rate-limitingfactor, and increasing concentrations did not increase biocidalefficiency. Griebe, T., Chen, C. I., Srinavasan, R., Stewart P.,“Analysis of Biofilm Disinfection By Monochloramine and Free Chlorine,”Biofouling and Biocorrosion In Industrial Water Systems (edited by G.Geesey, Z. Lewandowski, and H-C. Flemming), pp. 151-161, LewisPublishers (1994).

Excessive reactivity of pure free halogen donors was overcome by usingbromochlorodimethylhydantoin (BCDMH). The published study by M.Ludyansky and P. Himpler entitled “The Effect of Halogenated Hydantoinson Biofilms,” NACE, Paper 405 (1997), demonstrated higher efficacy onbiofilms compared to pure free halogen donors. However, while effective,it is still not an efficient halogen source when applied to biofilm.

Others have attempted to suppress biofilm growth in aquatic systems byusing an oxidizing halogen with the addition of adjuvant. U.S. Pat. No.4,976,874 to Gannon et al., incorporated herein by reference, disclosesa method and formulation for the control of biofouling using anoxidizing halogen in combination with a non-oxidizing quaternaryammonium halide. However, this method poses environmental issues.

Thus, the control of biofilm in aquatic systems has typically involvedthe addition of oxidizing and non-oxidizing biocides to bulk water flow.However, high levels of these expensive chemicals are needed becausetheir effectiveness is rapidly reduced as a result of exposure to thevarious physical and chemical conditions in specific applications sincethe concentration of the biocides is considerably reduced by the timethe biocides reach the biofilm.

SUMMARY OF THE INVENTION

The present invention is directed to a method of disintegrating biofilmpresent in aqueous medium and controlling the odor attendant to itsformation. The method comprises adding one or more chlorinatedhydantoins, specifically, monochlorodimethylhydantoin (MCDMH) ordichlorodimethylhydantoin (DCDMH), to the aqueous medium. Of particularimportance is that the chlorinated hydantoins' activity against biofilmis not lessened in the presence of sunlight, since thehalogen-stabilized active chlorine solutions are strikingly photostable.The concentration of the chlorinated hydantoins maintained in theaqueous medium generally ranges from about 0.01 to about 100 ppm(expressed as Cl₂) for biofilm inhibition.

In a concentrate, the concentration of the chlorinated hydantoinsgenerally ranges from about 0.1 up to 100% by weight based on the totalweight.

The present invention has application to essentially all aqueous systemscontaining or having the potential to contain biofilm. These may becooling water; pulping or papermaking systems, white water treatment,including those containing bulked activated sludge; and air washersystems; as well as agricultural potable and drainage systems; foodpreparation and cleaning systems; brewery, dairy and meat-producingsystems; and oil industry systems. Aqueous systems also include anypotable water systems, including drinking water systems; as well asrecreational water systems, such as swimming pools and spas; householdwater-related systems, including toilet bowls, drains, sewers, showerstalls, bathtubs, and sinks; as well as institutional “water-related”systems, hospital systems, dental water systems and any system where amedical device is in contact with an aquatic medium; ornamentalfountains, aquariums, fisheries, in aquaculture, and any other systemsubject to the growth of biofilm. The biofilm may comprise differentforms and species of pathogenic microorganisms, e.g., Legionellapneumophila, adhered or not adhered to surfaces, such as mats, flocs andslime.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the effect of NaOCl on heat transfer resistance (HTR)which correlates to biofilm formation and accumulation and dissolvedoxygen (DO) level in an aqueous system.

FIG. 2 illustrates the effect of NaOBr on heat transfer resistance (HTR)and dissolved oxygen (DO) level in an aqueous system.

FIG. 3 illustrates the effect of BCDMH/MEH on heat transfer resistance(HTR) and dissolved oxygen (DO) level in an aqueous system.

FIG. 4 illustrates the effect of MCDMH on heat transfer resistance (HTR)and dissolved oxygen (DO) level in an aqueous system.

FIG. 5 illustrates the effect of DCDMH on heat transfer resistance (HTR)and dissolved oxygen (DO) level in an aqueous system.

DETAILED DESCRIPTION OF THE INVENTION

The extent and nature of biofilm removal and disintegration, of course,vary with the context of the problem. The diverse nature of the problemsand the diverse environments in which biofilms grow call for a varietyof tactics and strategies for biofilm removal. With respect to anestablished biofilm, it is often desirable to remove it rather than tomerely sterilize and leave it in situ. In addition, it may be importantto kill the cells forming the biofilm and prevent them from spreading toother locations. Thus, for purposes of the present invention, the term“disintegration” of biofilm includes the removal and break-up ofexisting biofilm and the prevention of biofilm microorganism regrowth ina treated system. This is a more difficult task than “biofilm control”which includes both the prevention of biofilm growth from a clean systemand the prevention of continued growth in a treated system upon whichbiofilm has already formed.

The term “chlorinated hydantoin” refers to an hydantoin which may be inthe form of a pure compound, such as monochlorodimethylhydantoin or anadmixture of hydantoins, i.e., monochlorodimethylhydantoin anddichlorodimethylhydantoin mixtures, or mixtures of hydantoins withdegree of halogenation between 0.1 and 2.0.

The alkyl moieties of the chlorinated hydantoin may be the same ordifferent, preferably alkyl groups having 1 to 6 carbon atoms.

Preferred chlorinated hydantoins include, but are not limited to,dichloro-5,5-dimethylhydantoin (DCDMH), monochloro-5,5-dimethylhydantoin(MCDMH), dichloro-5-methyl-5-ethylhydantoin (DCMEH),monochloro-5-methyl-5-ethylhydantoin (MCMEH), and any combination of anyof the foregoing. The chlorinated hydantoin may be in the form of asolid, liquid, slurry, or gel. The term “solid” includes powders,granules, tablets, briquettes and slurries.

Concentrates of the chlorinated hydantoin have concentrations of activeingredients greater than typical biofilm control concentrates. Forexample, a solid concentrate of chlorinated hydantoin typically contains70% by weight of active ingredient (expressed as Cl₂) based upon 100%total weight of concentrate. In contrast, liquid concentrates of sodiumhypochlorite typically comprise only about 12% by weight of activeingredient based upon 100% total weight of concentrate. Additionally,the chlorinated hydantoins of the present invention are stable, unlikemost bleaches currently sold.

While the above discussion refers to the treatment of an aqueous systemcontaining biofilm with the chlorinated hydantoin, it is alsocontemplated that the aqueous system be formed after a dry biofilm orbiofilm in a non-aqueous medium is brought in contact with a solid orgranular halogenated hydantoin. In such instance, the aqueous system maybe formed by the addition of water or water vapor to the two solids orwater-free materials.

The amount of the chlorinated hydantoin added to the aqueous medium issufficient to disintegrate the biofilm. This is generally from about0.01 to about 100 ppm (expressed as Cl₂), preferably from about 0.05 toabout 25 ppm (expressed as Cl₂).

In addition to adding the pre-formed halogenated hydantoin to theaqueous system, it may be desirable to form the halogenated hydantoin insitu. This can be done by adding an hydantoin and an halogenating agentto the biofilm containing aqueous system separately in the appropriatemolar ratio. For example, an alkali metal hypochlorite (e.g., NaOCl) orchlorine gas or another active chlorine source and dimethylhydantoin canbe added in a molar ratio sufficient to form in situ the desired amountof the halohydantoin. Broadly, the molar ratio of chlorine (from thechlorine source) to alkylated hydantoin is from 1:100 to 100:1,preferably from 1:10 to 10:1.

In some systems, such as cooling water systems, additives are alwaysused. In other systems, such as swimming pools, there may be noperformance additives.

Performance additives (i.e., compositions that enhance the quality anduse of the chlorinated hydantoins) include, but are not limited to,cleaning agents, biodispersants, solubility modifiers, compaction aids,fillers, surfactants, dyes, fragrances, dispersants, lubricants, moldreleasers, detergent builders, corrosion inhibitors, chelants,stabilizers, bromide sources, and scale control agents. An importantrequirement is that the material be compatible with the chlorohydantoincomposition.

Solubility modifiers which may be added to chlorinated hydantoinsdescribed herein include, for example, sodium bicarbonate, aluminumhydroxide, magnesium oxide, barium hydroxide, and sodium carbonate. SeeU.S. Pat. No. 4,537,697. Solubility modifiers can be used in thecompositions in an amount ranging from 0.01% to 50% by weight.

Examples of compaction aids are inorganic salts including lithium,sodium, potassium, magnesium, and calcium cations associated withcarbonate, bicarbonate, borate, silicate, phosphate, percarbonate, andperphosphate. See U.S. Pat. No. 4,677,130. Compaction aids can be usedin the compositions in an amount ranging from 0.01% to 50% by weight.

Fillers which may be added to the chlorohydantoins include, for example,inorganic salts, such as lithium, sodium, potassium, magnesium andcalcium cations with sulfate, and chloride anions, as well as otherinorganics such as clays and zeolites. Fillers are used in compositionsto reduce product costs and can be added in an amount ranging from 0.01%to 50% by weight.

The biodispersant enhances the efficacy of the chlorinated hydantoin asa biofilm control agent and assists in maintaining the surfaces of thecontainer in which the aqueous medium is contained clean. They aretypically surfactants and preferably surfactants with a non-biocidaleffect on microorganisms and biofilms. Examples of biodispersantsinclude Aerosol OTB (sodium dioctyl sulfosuccinate), disodium laurylsulfosuccinate, sodium lauryl sulfoacetate, as well as other sulfonates.Surfactants are used in the compositions to enhance cleaning performanceand can be added in an amount ranging from 0.01% to 20% by weight.Generally, such a mixture contains from about 80% to about 99.99% byweight of chlorinated hydantoin and from about 0.01% to about 20% byweight of biodispersant, based upon 100% total weight of mixture;preferably, from about 90 to about 99.99% by weight of chlorinatedhydantoin and from about 0.01% to about 10% by weight of biodispersant.

An aqueous solution of the desired non-chlorinated hydantoin(s) at thedesired mole ratios may be prepared by the methods described in U.S.Pat. No. 4,560,766, and Petterson, R. C., and Grzeskowiak, V., J. Org.Chem., 24,1414 (1959) and Corral, R. A., and Orazi, O. O., J. Org.Chem., 28, 1100 (1963), both of which are hereby incorporated byreference.

EXAMPLE 1 Biofilm Inhibition Control Efficacy

The efficacy of biocides and biocides with dispersants was estimated bya reduction of biofilm dry weight in test flasks, compared to untreatedcontrols. Biofilm development was determined gravimetrically by themethods described in Ludyansky, M., Colby, S., A Laboratory Method forEvaluating Biocidal Efficacy on Biofilms, Cooling Tower Institute, PaperTP96-07 (1996).

The sheathed Sphaerotilus natans (ATCC 15291), which is known to be veryresistant to any chemical control and found in a variety of applications(cooling water systems, paper process waters, and sewage treatmentprocesses), was used in the tests.

The bacteria were cultivated at 25-30° C. in a 5% CGY medium whichcontained: 5 g of casitone (Difco), 10 g of glycerol, and 1 g of yeastautolysate (Difco) per liter of DI water. The inocula containedapproximately 10⁶ cells per milliliter. 8 oz. flasks were filled with150 ml of 5% CGY media and 1 ml of Sphaerotilus natans inoculum. Theflasks were filled with the test biocides, namely, NaOCl, NaOBr, MCDMH.Additional flasks, not containing a biocide, served as controls. Theflasks were installed on a shaker and maintained at 22-30° C. rotatingat 100-200 rpm for 48-72 hours. The contents were dried for 5 hours at105° C. and cooled overnight. The difference between the weight of theflasks containing the dried biomass and the tare weight of the flasksrepresented the dry biofilm mass.

The effectiveness of biofilm prevention was calculated as a percentchange in growth based on the difference between the average driedbiofilm weight in the untreated controls and in the treated flasks,according to the following formula:E %=(B_(control avg)−B_(avg))/B_(control avg)*100, where E %=percentreduction of biofilm growth, B=Biofilm weight, andB_(control)=Biofilm weight in the control flask.

The results of the experiments, including the concentration of thebiocides, are set forth in Table 1:

TABLE 1 Biocide Concentration, ppm B avg, g B control avg, g E, % NaOCl10 0.0028 0.0185 84.86 NaOBr 10 0.0013 0.0185 92.97 MBDMH 10 0.00080.0185 95.7 MCDMH 10 0.0005 0.0185 97.3 DCDMH 10 0.0005 0.0173 97.1NaOCl 5 0.009 0.0144 37.5 NaOBr 5 0.0021 0.0144 85.4 MBDMH 5 0.00810.0152 46.7 MCDMH 5 0.0007 0.0144 95.1 DCDMH 5 0.0009 0.0173 94.8The results show that chlorinated hydantoin (MCDMH) was a superiorbiofilm inhibition agent over free halogen donors (NaOCl or NaOBr).

EXAMPLE 2 Biofilm Removal Control Efficacy

Sphaerotilus natans (ATCC 15291), as in Example 1, was used in the testsdescribed below.

Biofilm Test System

An on-line testing system for chlorinated biocide efficacy testing wasused to provide a real-time, non-destructive method for biofilmmonitoring and measurement. The system monitors the heat transferresistance (HTR) which correlates to biofilm formation and accumulation,and dissolved oxygen (DO) level in the bulk water which correlates withchanges in biofilm activity. The system design, parameters and growthconditions are disclosed in Ludensky, M., “An Automated System forBiocide Testing on Biofilms.” Journal of Industrial Microbiology andBiotechnology, 20:109-115 (1998).

The system consisted of a continuous-flow heat-exchange loop, abiological growth reactor (chemostat) and subsystems for life support,biofilm measurement, and environmental control. All system parameters,including water flow, temperature, dilution rate and nutrientconcentration, were optimized for obtaining fast, heavy and reproduciblebiofilm growth. The system make-up water was kept at constant oxygensaturation (by continuous sparging of air), temperature, and pHconditions. Thus, any changes in DO concentrations or pH levels in therecirculating water were considered due to biofilm activity. Allmonitoring and control parameters were calculated in the dataacquisition system, which was controlled by a custom-designed computersoftware program. Data was collected every 15 seconds, with averagescalculated and recorded every 3 to 60 minutes in a spreadsheet forsubsequent graphical analysis. The program was designed so that thesystem was able to function continuously under constant conditions forseveral weeks. Biocide efficacy testing was conducted through analysisand comparison of the shape and values of the corresponding curves ofHTR and DO. Analysis included consideration of curve patternscorresponding to biocide treatment, as well as biofilm recovery(regrowth).

Growth Conditions

The sheathed Sphaerotilus natans (ATCC 15291), known to form a tenaciousbiofilm on heat exchanger surfaces in cooling water systems andpapermaking machines, was selected for biofilm growth. Inocula werepumped into the microbial growth reactor and allowed to sit at roomtemperature overnight. The next day, make-up water and nutrient (CGYmedia) were added. Selection of initial growth conditions and parametersof the system was based on previous experience, laboratory limitations,geometric size of the system's components, and the desire to promote agrowth of biofilm. Shifting of growth conditions from planktonic growthto attached filamentous growth was obtained by lowering mediaconcentrations to less than 5% and maintaining dilution rates higherthan maximum specific rate. Test conditions are shown in Table 2.

TABLE 2 Bioflim System On-Line Test Conditions Parameter Conditions pH7.2-8.5 Temp., circulating water 74-76° F. Temp., wall 85° F. Makeupwater Clinton tap Substrate concentration CGY; 30-70 ppm Inoculum S.natans Water flow 3 fps Dilution rate 0.9 Make up water 170 ml/minNutrient addition 1 ml/min System volume 10 litersBiocidal efficacy of the test solutions was determined by analysis ofthe shape of the HTR and DO curves indicating the biofilm's response tobiocidal treatments.Treatment Programs

During treatment programs, the system was continuously fed with nutrientand make-up water (constant chemistry, oxygen and temperature). Threemodes of treatments were tested, namely, slug, slug plus continuous, andcontinuous.

Slug treatment was conducted by the addition of a prepared stocksolution in a precalculated dose (per volume of the circulating water inthe system) to the chemostat. In the slug plus continuous mode, biocidetreatment was carried out by an initial slug dose injected to overcomehalogen demand, followed by a continuous, 3-hour treatment at a constantconcentration based upon the makeup water rate.

Biocide Preparation and Monitoring

All five biocides, NaOCl, NaOBr, MCDMH, BCDMH/MEH, and DCDMH, wereprepared as 1000 ppm fresh Cl₂ master solutions. Treatmentconcentrations for all biocides were calculated from the measurement offree and total residual halogen, as measured by the DPD Cl₂ test,conducted immediately before treatment.

Tests incorporating repeated slug plus continuous treatments atincreasing initial concentrations (10, 15 and 20 ppm) were performed forthree consecutive days on NaOCl, NaOBr, MCDMH, BCDMH/MEH, and DCDMH.Heat transfer rate and dissolved oxygen levels in the system wereautomatically monitored and their dynamics were analyzed. Based onobtained parameters, the following conclusions were reached:

NaOCl, NaOBr, and BCDMH/MEH were not able to remove biofilm at any ofthe tested concentrations. Biofilm recovery was observed 24 hours afterthe start of each treatment and HTR values were higher than valuesobserved at the start of each treatment, as shown in FIGS. 1, 2 and 3.

Dissolved oxygen response to biocide treatment was the strongest in thecase of DCDMH, and the weakest in the case of NaOCl. Through analysis ofcurve patterns (FIG. 1-FIG. 5), it was concluded that biofilm regrowthcontrol could be achieved by a slug plus continuous treatment of 15 ppmBCDMH/MEH or 20 ppm of NaOBr as shown in FIG. 2 and FIG. 3. However,neither of these biocides was able to initiate biofilm removal.

Testing of chlorinated hydantoins MCDMH and DCDMH demonstrated a uniqueeffect: biofilm sloughing occurred soon after addition of 20 ppm ofeither MCDMH or DCDMH. The results of the tests are shown in FIG. 4 andFIG. 5. This effect is not common for any other oxidizing biocides.

The observations set forth above are summarized in the following table:

TABLE 3 Slug Plus Continuous Treatment Biofilm Control Biofilm RemovalHTR DO HTR NaOCl Not effective Weakest No NaOBr Effective at 20 ppmModerate No BCDMH/MEH Effective at 15 ppm Moderate No MCDMH Effective at15 ppm Moderate Yes at 20 ppm DCDMH Effective at 15 ppm Strongest Yes at20 ppm

EXAMPLE 3

This example demonstrates the enhanced photostability of MCDMH ascompared to NaOCl when test solutions thereof are exposed to simulatedsunlight.

Test solutions were prepared by adding to tap water having a temperatureof 22° C. and a pH of 7.8 NaOCl and MCDMH at the concentrationsindicated in Table 4 below. These solutions were illuminated by UVA-340fluorescent lights that simulate the spectral radiance of the sun at thesurface of the earth. The test samples were covered with quartz plates,transparent to ultraviolet light, to prevent evaporation. Total halogenconcentrations were measured as a function of time. The generated activehalogen decay curves were analyzed using first order kinetic algorithmsand the corresponding active halogen half-lives calculated. The resultsare shown in Table 4.

As shown in Table 4, MCDMH provides dramatically superior photostabilityto NaOCl. The observed active halogen half-life for MCDMH was 108 hourscompared to 1.1 hour for NaOCl.

TABLE 4 Photolysis of MCDMH and NaOCl Solutions Total Halogen (ppm asCl₂) Delta Time (hr) NaOCl MCDMH 0 4.0 5.9   1.5 1.1 5.6   6.5 0.07 5.3 29.5 — 4.1  52.5 — 3.1 100  — 2.3 187  — 1.5 267  — 1.0 First orderhalf-life (hr) 108 1.14

These data clearly show that the activity of MCDMH dropped negligiblyfor the first 6.5 hours and significant activity remained for theduration of the test, while the NaOCl's activity dropped precipitouslyin the presence of the simulated sunlight. The comparative half-livesfurther show the remarkable photostability of the chlorinated hydantoin.

EXAMPLE 4

Hydantoin-stabilized active chlorine solutions can likewise be generatedby combining hydantoins with NaOCl. As shown in Table 2, combinations ofDMH and NaOCl produce greater photostability than even combinations withcyanuric acid, a well-known chlorine photostabilizer for therecreational water market. The test conditions were the same as those ofExample 3.

TABLE 5 Photostability of Hydantoin and Cyanuric Acid StabilizedHypochlorite Solutions Total Halogen (ppm as Cl₂) NaOCl + NaOCl + DeltaTime (hr) 30 ppm DMH 30 ppm Cyanuric acid 0 4.6 4.3   1.5 4.3 4.1   6.54.05 3.6  29.5 3.6 2.0  52.5 3.0 0.78 100  2.2 0.07 187  1.68 — 267 1.19 — First order half-life (hr) 141 17

The data in Table 5 show that DMH dramatically enhances thephotostabilization of NaOCl and the combination performs better that theNaOCl and cyanuric acid. The observed active halogen half-life for theNaOCl+DMH stabilized solution was 141 hours as compared to 17 hours forcyanuric acid stabilized NaOCl.

1. A method of disintegrating biofilm in an aqueous system, whichcomprises adding to or forming in an aqueous medium of the aqueoussystem containing the biofilm a chlorinated hydantoin comprising amonochlorodialkylhydantoin, dichlorodialkylhydantoin or a mixturethereof in an amount sufficient to disintegrate the biofilm and removethe biofilm from surfaces in said aqueous system, wherein the alkylgroup of the chlorinated hydantoin contains from 1 to 6 carbon atoms. 2.The method of claim 1, wherein the chlorinated hydantoin ismonochlorodimethylhydantoin, dichlorodimethylhydantoin, or a mixturethereof.
 3. The method of claim 1, wherein the chlorinated hydantoin isadded to the aqueous medium as a solution or an aqueous slurry.
 4. Themethod of claim 1, wherein the chlorinated hydantoin is added to theaqueous medium as a solid.
 5. The method of claim 1, wherein the treatedaqueous medium is exposed to sunlight.
 6. The method of claim 1, whereinthe chlorinated hydantoin is formed in situ by adding to the aqueousmedium chlorine from a chlorine source and an alkylated hydantoin in amolar ratio of chlorine to alkylated hydantoin of from 1:100 to 100:1.7. The method of claim 6, wherein the molar ratio of chlorine toalkylated hydantoin is from 1:10 to 10:1.
 8. The method of claim 1,wherein the aqueous medium contains biofilm adhering to a substrate. 9.The method of claim 1, wherein the chlorinated hydantoins are added withperformance additives.
 10. The method of claim 9, wherein theperformance additives are dispersants, biodispersants, scale controlagents, corrosion inhibitors, surfactants, biocides, cleaning agents,and mixtures thereof.
 11. The method of claim 1, wherein the aqueoussystem is a cooling water system, a pulping or papermaking system, anair washer system, an agricultural potable and drainage system, a foodpreparation or cleaning system, an oil industry system, a potable watersystem, a household water-related system, or an institutionalwater-related system.
 12. The method of claim 1, wherein the chlorinatedhydantoins are in an amount sufficient to form a concentration of fromabout 20 ppm to about 100 ppm (expressed as Cl₂) of the chlorinatedhydantoins in the aqueous medium.
 13. The method of claim 1, wherein thechlorinated hydantoin is dichloro-5,5-dimethylhydantoin (DCDMH),monochloro-5,5-dimethylhydantoin (MCDMH),dichloro-5-methyl-5-ethylhydantoin (DCMEH),monochloro-5-methyl-5-ethylhydantoin (MCMEH), or a mixture thereof. 14.The method of claim 1, wherein the aqueous system is a system subject tothe growth of biofilms.
 15. A method of removing biofilm from asubstrate in an aqueous medium which comprises: adding to or forming insaid aqueous medium monochlorodimethylhydantoin,dichlorodimethylhydantoin, or a mixture thereof in an amount sufficientto remove the biofilm from the substrate in the aqueous medium.
 16. Themethod of claim 15, wherein the chlorinated dimethylhydantoin is formedin situ by adding to the aqueous medium chlorine from a chlorine sourceand dimethylhydantoin in a molar ratio of chlorine to dimethylhydantoinof from 1:10 to 10:1.
 17. The method of claim 16, wherein the chlorinesource is sodium hypochlorite or gaseous chlorine.